I absolutely love free and open source software and use it as much as possible, sometimes even contribute to it!
So, when my dad brought me a DVD today I wanted to be able to play it on my main OS, which is (k)ubuntu. The answer, which came from Ask ubuntu is really simple!
First run
sudo apt-get install libdvdread4
(or use your preferred package manager to install libdvdread4. You may find it’s already installed, don’t worry about it and move on to the next step)
Now run
sudo /usr/share/doc/libdvdread4/install-css.sh
This second command was actually what fixed it for me. Bingo, I get to play dad’s DVD!